1. Field of the Invention
The present invention relates to a rotary developing device in the field of an electrophotographic full color image forming apparatus.
2. Description of the Related Art
Three developing units in which developers (each containing toner and carrier) of three primary colors are filled respectively are mounted on the electrophotographic full color image forming apparatus. Alternatively, such an image forming apparatus may be further provided with another developing unit in which a black developer is filled. These developing units are arranged such that they face one or a plurality of photosensitive drums in an opposing manner. Image forming is carried out by visualizing or developing electrostatic latent images with a plurality of developers which are applied in sequence.
In general, in case downsizing and lowering of the cost of the device are emphasized, a mechanism is adopted where a revolver holding four developing units is arranged in the vicinity of a photosensitive drum and by rotating this revolver, respective developing units are moved in sequence to a position where these developing units face the photosensitive drum in an opposing manner and electrostatic latent images are visualized or developed with respective developing units.
In such a mechanism, tracking rollers which are mounted on developing rollers of the developing units coaxially come into contact with the surface of the photosensitive drum so as to hold the distance between the developing rollers and the photosensitive drum constant.
With such a construction, in case an impact which the tracking roller receives when it comes into contact with the photosensitive drum is large, a turbulence of image occurs. Accordingly, a method has been proposed to remove the tracking roller and to fix the developing units to the revolver using screws.
In this method, however, an adjustment of mounting positions of the developing units to the revolver (an adjustment of the distance of developing units relative to the photosensitive drum) becomes cumbersome. Furthermore, to eliminate changing of position of the photosensitive drum at the time of replacing the photosensitive drum, it is necessary to increase the rigidity of the device. Furthermore, the rigidity of the revolver must be increased to eliminate shifting of the developing units and slacking of screws due to a centrifugal force and hence, the mechanism becomes complicated thus the device becomes large-sized and requires considerable man-hours for the adjustment.
The present invention has been made in view of the above and it is an object of the present invention to provide a rotary developing device which facilitates the adjustment of positioning of the developing units, causes no shifting of the developers even after the use of a long period and has a simple mechanism.
The foregoing and other objects and novel features of the present invention will be made clear hereinafter in view of the description of the specification and attached drawings.